US2329762A - Vehicle brake control system - Google Patents

Description

Sept. 21, .1943. D. R. BORST ET AL VEHICLE BRAKE CONTROL SYSTEM Filed ijeb. 25, 1942 INVENTORS Claude Mjiines BY QM ATTORNEY Douglas E- Patented Sept. 21, 1943 2,329,762 VEHICLE BRAKE CONTROL SYSTEM Douglas R. Borst, Pitcairn,

Pa., assig'nors Air Brake Company, W ration of Pennsylvania Pittsburgh,

and Claude M. Hines, to The Westinghouse ilmerding, Pa., a corpo- Application February 25, 1942, Serial No. 432,188

11 Claims.

This invention relates to brake control systems for vehicles, such as railway cars and trains, and has particular relation to brake control systems including apparatus for detecting the slipping condition of individual wheels or wheel units of the vehicle and for so controlling the brakes associated with those wheels as to prevent sliding thereof.

The term slipping condition a applied herein to a. vehicle wheel refers to the rotation of the exceed the limit of adhesion between the wheel and the road surface or rail. When a wheel begins to slip, it decelerates at an abnormally rapid rate and unless the degree of application of the brakes applied to the wheel is instantly and rapidly reduced the wheel reduces in speed to a locked condition and slides. The term sliding or sliding condition is thus employed herein to designate the locked or non-rotative condition of the vehicle wheel at a time that the vehicle is in motion. It is obviously desirable to prevent the sliding of vehicle wheels in order to prevent the development of flat spots on the wheels necessitating repair or replacement of the wheel.

A vehicle wheel, such as a railway car wheel, cannot greatly exceed a certain rate of rotative deceleration, such as a rate correspondin to a rate of retardation of the car or train of four or five miles per hour per second, without slipping. If, therefore, the wheel rotatively d'ecelerates at a rate in excess of a rate corresponding to ten miles per hour per second it is a positive indicain a slipping condition. It is thus possible to detect a slipping condition of the wheel at its inception by a means responsive to the rate of deceleration of the wheel.

Various devices and apparatus responsive to the rate of rotative deceleration of a vehicle wheel have previously been proposed and employed for the purpose of detecting the slipping condition of a vehicle wheel for a desired purpose, such as the rapid reduction in the degree of application of the brakes associated with the wheel to prevent sliding of the wheel.

It is an object of our invention to provide a vehicle brake control system including a novel arrangement for detecting the slipping condition of a plurality of different wheel units and controlling the brakes associated with these Wheel units in a manner to prevent the sliding of the wheels.

More specifically, it is an object of our inventionto provide a vehicle brake control system of the type indicated in the foregoing object and further characterized by a control relay having a plurality of separate windings each of which is energized in accordance with the rate of de celeration of a corresponding wheel unit, the windings cooperating in a. manner to effect an operative response of the relay only when one or more of the Wheel units begins to slip.

Another object of our invention is to provide a vehicle brake control system of the type indicated in the foregoing objects whereby the reduction of the degree of application of the brakes associated with the slipping wheel is initiated only When the wheels exceed a certain high rate of rota-tive deceleration and is continued thereafter as long as the wheels exceed a certain low rate of deceleration.

It is another object of our invention toprovide a vehicle brake control system of the type indicated in the foregoing objects and characterized further in that the restoration or reapplication of the brakes occurring in response to the drop-out of the control relay is automatically restricted to a relatively low rate.

The above objects, and other objects of our invention which will be made apparent herein after, are attained by means of the simplified brake control system diagrammatically shown in the single figure of the accompanying drawing.

Description Referring to the drawing, the brake control equipment shown is of the familiar straight-air type of fluid pressure brake control apparatus effective to control the brakes associated with two wheel trucks H and ii of a single car. Each of the wheel trucks comprises two wheel units, each unit having a pair of wheels l3 fixed at opposite ends of a connecting axle. Only one wheel of each WETREEI unit is visible in the drawing. Although employed herein to designate a pair of axle-connected Wheels, the term wheel unit may refer also to a single wheel or any other number of connected wheels.

The brakes associated with the wheels I 3 may be of an suitable type, such as the conventional clasp-arranged shoes engaging the rim of the wheels and operative through the medium of brake levers or rigging in response to the supply of fluid under pressure to and the release of fluid under pressure from brake cylinders I4. Although any number of brake cylinders may be provided, one brake cylinder is illustratively shown for each wheel unit in substantially vertical alignment above the corresponding unit.

The fluid pressure brake control apparatus shown comprises a train pipe, hereinafter referred to as the control pipe it, a source of fluid under pressure hereinafter referred to as the main reservoir 56, and a brake valve 6'! of the self-lapping type.

The brake valve H is of the well-known type described in detail and claimed in Patent 2,042,112 of Ewing K. Lynn and Rankin J. Bush and is therefore shown only in outline form and will be here but briefly described,

Brake valve l'l comprises suitable self-lapping valve mechanism having a rotary operating shaft to which an operating handle Ha is fixed. In the normal or brake release position of the brake valve handle i'la, fluid under pressure is exhausted from the control pipe it to atmosphere through an exhaust port and pipe 48 at the brake valve. Upon the displacement of the brake valve handle in a horizontal plane out of its brake releaseposition into its so-called application zone, the exhaust communication just mentioned is closed and a supply communication is established through which fluid under pressure is supplied from the main reservoir It to the control pipe 15; The nature of the self-lapping valve mechanism of the brake valve ll is such that the pressure established in the control pipe i is substantially proportional to the degree of displacement of the brake valve handle out of its brake release position. The valve mechanism of the brake valve l'i, moreover, possesses a pressure-maintaining feature for maintaining a application of the pressure in the control pipe l5 corresponding to the position of the brake valve handle in the event that the pressure in the control pipe tends tofreduce for any reason, such as leakage.

The brake cylinders It for each of the wheel trucks are connected by corresponding branch pipes Ilia to the control pipe it, each of the branch pipes I511 having a control valve mechanism I9 interposed therein for a purpose hereinafter to be described.

Control valve. mechanism 19 is of the type shown and described in detail in the copending application Serial No. 381,083 of Joseph C. McCune, filed February 28, 1941, and now Patent 2,283,608, assigned to the assignee of the present application. Since reference may be had to the patent just referred to for details of construction and operation of control valve mechanism l9 it is shown in outline form only herein and will be but briefly described.

Essentially, the control valve mechanism 59 con'rprises pneumatically operated supply and release valves, under the control of a magnet alve having an electro-magnet winding or solenoid 2|. Normally, when the magnet winding 2i is deenergized, the supply valve is in open position establishing communication through the corresponding branch pipe that from the control pipe i5 to the brake cylinderslt. At the same time the release valve is closed.

Upon energization of the magnet winding 2!, the supply and release valves are substantially simultan'e'ously'operated to closed and opened positions, respectively, the supply valve cutting off-the communicationthrough the branch pipe I541 from the control pipe to the brake cylinders and the release valve opening an exhaust communication through which fluid under pressure is exhausted at afrapid rate from the brake cyimdersm "pantinvalve mechanism l9 also includes a reapplication control device which is effective to restrict to a relatively slow rate the supply of fluid under pressure through the branch pipe 15a to the brake cylinders as long as a certain differential pressure such as five pounds per square inch exists between the pressure in the control pipe l5 and the pressure in the brake cylinders M. The restriction of the ire-supply of fluid under pressure to the brake cylinder to a slow rate is automatically effective as hereinafter described following the reduction in the degree of brakes in response to slipping of the wheel and minimizes the possibility of the recurrence of wheel-slipping because a substantial pressure is not built-up in the brake cylinders until after theslipping wheels have been fully restored to vehicle speed.

In accordance with our present invention, there is further provided novel electric decelerometer apparatus for detecting the slipping condition of the wheels of each trucl; for the purpose of controlling the magnet winding ii of the control valve mechanism l9.

Specifically, theelectric decelerometer apparatus which we have provided for each wheel truck ii and it comprises two generators 22a and 22?) mounted in any suitable manner, as in the journal casing at the end of a wheel axle with the armature shaft of the generator coupled to the end of the axle in the mannerindicated in the drawing, so that the armatures of the generators are drivenin: accordance with the rotational speed of the correspondingwheel units. The generators 221a and 221) may be of any suitable type, such as the permanentmagnet field core type, so designed as to produce a voltage substantially proportional .to the rotational speed of the corresponding wheel unit, the polarity of the voltage at-the terminals of the generators reversing automatically upon reversal of rotation of the vehicle wheel.

In addition to the generators 22a and 221), the electric decelerometer apparatus for each wheel truck I! and i2 further comprisesa so-called slip relay 2 two electrical condensers 25a. and 25b and two adjustable resistors 26a and 2%.

Each of the slip relays Mis of the so-called unidirectional type having two separate windings a and b' respectively, two back contacts 0 and d and one front contact e; I It will be understood that, in the usual manner, the term back contact refers to a contact which is'in closed position when the armature of the relay is dropped-out and which are actuated to an open position upon pick-upof the armature of the relay. In a similar manner it will be understood that the term front contact refers to a contact which is in open position when the armature of the relay isdropped-out and which is actuated to a closedposition in response to the pick-up of-the relay armature.

As willbeapparent from the drawing without specific description, the winding aof each slip relay 24 is connected in series circuit relation with the corresponding condenser 25a across the terminals of the corresponding axle-driven genorator 22a, the resistor 260. being connected in shunt relation to the winding 0, by the back contact c of relay 2&- in its dropped out or closed position. In a similar manner, it will be seen that the winding bof each slip relay 24 is connected in series relation. with the corresponding condenser 25b across the terminals of the corresponding axle-driven generatorv 22b, resistor 25b being connected in shunt. relation to the winding b by back contact (1 of relay 24 in its dropped-out or closed position.

For reasons which will be made apparent hereinafter, the connections to the terminals of the generators 22a and 22b of the several wheel trucks H and I2 are automatically reversed in response to a reversal in the direction of rotation of the vehicle wheels by suitable means, illustrated as a reversing relay 35 of the polarized type. The reversing relay 35 has a winding a which is connected acrossthe terminals of one of the axle-driven generators, for example the generator 22a of wheel truck H, and a plurality of pairs of transfer or reversing contacts b and 0, one pair for each of the generators 22a, and 221).

When the vehicle is traveling in a forward direction, the polarity of the voltage at the terminals of generator 22a is such as to energize and maintain the position in which they are shown, Upon reverse travel of the vehicle and a of relay 35 is energized by the reversed current in a manner to actuate the contacts of the relay to the position opposite to that in which they are shown.

It will accordingly be apparent that notwithstanding a reversal of the polarity at the terminals of the axle-driven generators, due to the reversal of travel of the vehicle, a voltage of uniform polarity is impressed across each seriesconnected condenser 25a and winding 11. of slip relay 24 as well as across each condenser 25b and winding b of slip relay 24.

The front contact e of each slip relay 24 is connected in series relation with the magnet winding 2i of the corresponding control valve mechanism IS in a wire 28, one end of which is a positive bus wire 29 and the bus wire 3|, the bus wires 29 and 3| being connected respectively to the positive and negative terminals of a suitable source of direct-current, such as a storage battery 32, Contact e of each relay 24 accordingly controls energization and deenergization of the magnet winding 2| of the corresponding control valve mechanism 19.

An asymmetric device 33, which may be a halfway rectifier of either the dry disk or tube type, is connected in shunt relation to the magnet gizing circuit for the winding to minimize or prevent arcing or pitting of the contact 3 of relay 24.

When the vehicle wheels l3 accelerate rotatively in speed, the corresponding generators 22a d 22b supply a voltage which increases with the speed of the Wheels, thereby causing current to be supplied to charge the corresponding condensers 25a and 252) which current flows through the corresponding windings a and b of the slip relay 24 in a corresponding direction. It will be apparent that the current supplied to charge the condensers will vary substantially in proportion to the rate of increase of the voltage supplied by the generator and therefore substantially in proportion to the rate of rotative acceleration of the vehicle wheels.

On the other hand, when the vehicle wheels l3 rotatively reduce in speed, the corresponding which is connected to a negative rotative deceleration reduction of the voltage at the terminals of the enerators 22a and 22b causes the condensers 25a and 25b to discharge current reversely in the circuit through the armature winding of the generators and the corresponding windings a and b of the relay 24, which current is substantially proportional to the rate of rotative deceleration of the wheels.

The character of the relay 24 and the connections of its windings a and b are such that current supplied to charge the condensers 25a and 25b flows in such a direction through the windings as to bias the armature of the relay and consequently the contacts of the relay toward their dropped-out position, or if they are already in their dropped-out position, maintain them more firmly in such position. On the other hand, the current discharged from the condensers flows through the windings a and bin such a direction as to cause pick-up of the armature of the relay and a consequent actuation of the contacts to their picked-up position when a suificient number of ampere-turns is attained.

The number of turns in the separate windings a and b and the resistance thereof is such that the total number of ampere-turns of both windings produced in response to the maximum nonslipping rate of deceleration of the vehicle wheels is insufficient to cause pick-up of the contacts of the relay.

Whenever one or both of the wheel units of a given truck begin to slip, however, the rate of deceleration of the wheels is abnormally high and consequently the current discharged from the corresponding condenser is abnormally high. In such case, therefore, the total number of ampereturns exceeds that required to cause pick-up of the contacts of the relay and they are accordingly actuated to their picked-up position.

Relay 24 may be picked-up at a lesser rate of decelerationof the wheels when both wheel units slip simultaneously compared to the rate of deceleration at which it picks up when only one wheel unit of a given truck slips. This is so because with one wheel unit decelerating at a normal or non-slipping rate, the current energizing the corresponding winding of the relay 24 is relatively low, so that the current through the other winding corresponding to the slipping wheel unit must be relatively higher in order to cause pick up of the relay than when the current in both windings is abnormally high due to the slipping of both wheel units. Thus, for example, relay 25 may be picked-up upon slipping of only one wheel unit when such slipping wheel unit decelerates at a rate in excess of ten miles per hour per second whereas when both wheel units slip simultaneously the relay may pick up when either one or both of the slipping wheel units exceeds a rate of rotative deceleration of seven miles per hour per second.

In any event, however, the relay 24 is not picked-up unless one or both of the wheel units begins to slip.

When the relay 24 picks-up, the resistors 25a and 26b are disconnected from shunt relation with the corresponding windings a and b of the relay 24 in response to actuation of the back contact 0 and d to their respective pickedup or open positions. The current through the respective windings a and b of the relay 24 is thus proportionately increased for a given rate of of the corresponding Wheel units. For example, when the relay 24 is pickedup, the current through the windings thereof may be increased thirtyrotative deceleration in effect at lay is picked-up.-

It is well known that due to the reduction in the reluctance of the magnetic pathincluding the magnetic core of the relay and the movable armature when the armature of the relay is picked-up, the armature may be held picked-up by a lesser current than is required to cause pickup operation thereof. Thus relays 2Q may be so designed that the armature thereof will not dropout, once it is picked-up, until the total number of ampere-turns effective is reduced to fifty per cent of that required to cause pick-up of the armature.

It will be apparent, therefore, that inherently the relays 2d, remain picked-up after being once actuated to their picked-up position until such time as the rate-of rotative deceleration of the wheel units reduces below a value somewhat lower than that required to cause pick-up of the relays.

In order to provide a greater difierence between the rate of rotative deceleration of a wheel unit required to cause pick-up of the relay 2% and the rate below which drop-out oi the relay occurs than that inherent in the relay itself, resistors 26a and 2517 are provided. It will be apparent that due to the increase in the current energizing the respective windings a and b of the relay 2d resulting from the disconnection of the resistors demand 26b in response to pick-up of the relay, the amount of reduction in the rate of rotative deceleration of the wheel units which must be e'liected before drop-out of the relay 24 can occur issubstantially greater than that due merely to the inherent characteristic of the relay itself.

It will thus be seen that by adjusting the resistance of the resistors 26a and 25bto any desired value, energization of the windings a and b of relay ZA may be correspondingly controlled so as to maintain the relay picked-up over any desired range in the rate of rotative deceleration of the vehicle wheels. Thus resistors 25a and 2% may be so adjusted in value that in the case where only one wheel unit slips, the relay 24 is picked-up when the slipping wheel exceeds a rate of rotative deceleration exceeding ten miles per hour per second and not restored to its dropped-out position until the slipping wheel unit decreases below, for example, a rate of rotative deceleration of two miles per hour per second. Similarly, when both of the wheel units slip simultaneously, the relay 24 may be picked-up when one or both of the wheel units exceeds a rate of rotative deceleration of seven miles per hour per second and not restored toits dropped-out position until the slipping wheels decrease below a certain low rate of rotative deceleration such as 2.5 miles per hour per second.

per cent for a given rate'oi the time the re- Operation Let it be assumed that the car having the equipment shown in the drawing is traveling under power with the brake valve handle i'la in its brake release position, so-that the brakes are released, and that the operator desires to bring the car to a stop. To do so, he first shuts oi the propulsion power in the usualmanner and then shifts the brake valve handle Fla out or its brake release position into its application zone an amount corresponding to'the desired degree of brake application. The control pipe i5 is thus charged to a corresponding pressure as are the brake cylinders IA, to which fluid under pressure is supplied through the branch pipes 15a from the control pipe. The brakes are accordingly applied on the wheels to a degree corresponding to the pressure established in the brake cylinders.

As long as the wheels on the vehicle or car do not slip, no variation in the fluid pressure in the brake cylinders I l occurs except in accordance with variations of the pressure in the control pipe effected by the operator. If however, when an application of the brakes is initiated or at any time during a brake application, one or more of the wheel units on the car begin to slip, a further operation occurs which will now be described.

Let it be assumed that when the brakes are applied, the right-hand wheel unit of wheel truck II begins to slip. Slip relay 24 for wheel truck H is thus picked-up and the front contact e of the relay is effective in its picked-up or closed position to eliect energization of the magnet winding 2! of the control valve mechanism !9 for truck ll.

As previously explained, energization of the magnet winding 2! of the control valve mechanism It causes closure of communication through the branch pipe i511. to the brake cylinders 14 of wheel truck H and the venting of fluid under pressure from those brake cylinders.

The degree of application of the brakes associated with the two wheel units of wheel truck I l is thus promptly and rapidly reduced. Therate of rotative deceleration of the slippingwheel unit thus promptly decreases to zero after which the wheel unit accelerates at an abnormally rapid rate back toward a speed corresponding to car speed.

The slip relay 24 is maintained picked-up for reasons previously explained, until the rate of rotative deceleration of the slipping wheel unit decreases below a low rate, such as two miles per hour per second, whereupon the slip relay is restored to its dropped-out position. The reduction of the pressure in the brake cylinders 54 is thus reduced continuously from the time that the relay z iis picked-up until the time that the relay is restored to its dropped-out position. The amount of the reduction in brake cylinder pressure will vary with the initial pressure in the brake cylinder as well as the time that the relay 24 is picked-up. In any event, the interval of time that the relay 24 is picked-up is sufliciently short so as to permit only a partial reduction of the pressure in the brake cylinders and not a complete reduction of the pressure in the brake cylinders to atmospheric pressure. In other words, the arrangement is such as to produce a sufficient reduction of the pressure in'the brake cylinders to cause the slipping wheels to be restored to vehicle speed without unnecessary reduction of the pressure in the brake cylinders involving needless consumption or waste of fluid under pressure.

As previously explained, the deenergization of the magnet winding 2! of the control valve mechanism I9 in response to the drop-out of the relay 2 3 not only terminates the reduction of the pressure in the brake cylinder but conditions the control valve mechanism to reestablish communication through the branch pipe 15a in such a manner that fluid under pressure is resupplied to the brake cylinders at a restricted rate. The pressure in the brake cylinders l l on the truck having the wheel unit which slipped is accordingly built-up at a restricted rate.

As previously mentioned, the slipping wheels accelerate at an abnormally rapid rate back toward a speed corresponding to car speed in response to the reduction in the degree of application of the brakes effected by pick-up of the relay 24. Accordingly, the slipping wheels are restored fully to a speed corresponding to car speed before a substantial increase of the pressure in the brake cylinders can occur in response to the drop-out of the relay 24. As a matter of fact, the rate at which the pressure in the brake cylinders is restored may be so selected that a pressure corresponding to the pressure in the control pipe I is not attained in the brake cylinders for a considerable time after the slipping wheel unit has been restored to a speed corresponding to car speed.

The reapplication control device of the control valve mechanism I S continues effective to restrict the rate of resupply of fluid under pressure to the brake cylinders l4 until brake cylinder pressure is built-up to less than five pounds per square inch pressure below the pressure in the control pipe and is then restored to its original condition permitting the supply of fluid under pressure from the control pipev E5 to the brake cylinders at the normal or more rapid rate. s

The resupply of fluid under pressure from control pipe l5 to the brake cylinders M of the truck having the wheels which slipped tends to cause a reduction of the pressure in the control pipe. However, due to the pressure-maintaining feature or the brake valve IT, fluid under pressure is supplied automatically to the control pipe to maintain a pressure therein corresponding to the position of the brake valve handle and to compensate for the fluid under pressure supplied to the brake cylinders.

Upon the drop-out of the relay 24, the resistors 26a and 26b are reconnected into shunt relation with the correspondin windings a and b .of the relay 24, thereby reconditioning the relay to be picked-up thereafter only in response to a slipping condition of either one or both of the wheel units of the corresponding truck.

Due to the fact that the pressure is increased in the brake cylinders M at a restricted rate by the control valve mechanism l9 following a wheel slip condition repeated slipping of the same wheel unit is unlikely. 'However, in the event that the wheels of a truck again begin to slip upon the restoration of an increased pressure in the brake cylinders following a previous slipping condition, the above operation is repeated so that at no time are the wheels permitted to reduce in speed to a locked condition and slide.

In the previously described operation, it was assumed that only one wheel unit of a truck began to slip when the brakes were applied. In the event that both wheel units of a given truck being to slip substantially simultaneously when the brakes are applied or at any time during a brake application, the slip relay 24 is similarly picked-up in response to the abnormal or slipping rate of rotative deceleration of the wheel units. As previously pointed out, however, the relay 24 will pick-up at a somewhat lower rate of rotatlve deceleration of the wheel units than in the case where only one wheel unit slips. The magnet winding 2| of the control valve mechanism i9 is in any event energized, as in the previous instance, to efiect a reduction of the pre sure in the brake cylinders and a subsequent restoration of the pressure therein at a restricted rate when the relay 24 is restored to its droppedout position. As previously pointed out, the relay 24 may drop-out at a rate of wheel deceleration which is slightly higher than in the case of slipping of only one wheel unit. Thus although the range of decelartion rates over which the relay 24 is picked-up may be different in amount when both wheel units slip simultaneously as compared to when only one wheel unit slips, the interval of time that the relay 24 is picked-up is suflicient to cause such a reduction of the pressure in the brake cylinders as to insure the restoration of the slipping wheels back to a speed corresponding to car speed.

In the event that either one or both of the wheel units of wheel truck l2 begins to slip when the brakes are applied or during a brake application, the slip relay 24 associated with that truck is picked-up and the control valve mechanism l9 associated therewith operated to effect a rapid reduction of the pressure in the brake cylinders l4 for the wheel truck l2 in a manner similar to that described for wheel truck ll. Since the operation of the electric decelerometer apparatus and the brake control apparatus for wheel truck I2 is identical to that for wheel truck I I, such operation is not repeated in detail.

When the car comesto a complete stop the slip relays 24 are always restored to their dropped-out positions, if not previously restored thereto, because of the cessation of the supply of voltage from the axle-driven generators 22a and 22b. Consequently the control valve mechanisms l9 are always conditioned while the car is at a standstill for charging the brake cylinders I4 to the pressure established in the control pipe 14. Accordingly, it will be seen that when the ing to the pressure established in the control pipe I 5. Obviously the operator may vary the pressure in the control pipe l5 when the car is at a standstill to secure any desired degreeof application of the brakes for holding the car on any grade encountered in service.

When the operator again desires to start the car he first releases the brakes merely by restoring the brake valve handle IIa to its brake release position. Fluid under pressure is accordingly eX- hausted by flow reversely from the brake cylinthe control valve mechanism l9 to pipe I5 and thence to atmosphere through the exhaust port and pipe H3 at the brake valve. Upon the restoration of atmospheric pressure in the control pipe [5, the brakes are correspondingly completely released.

If the car travels in a reverse direction, the

of polarity of the voltage at the terminals of the generators, the condensers are always subject to a charging voltage of uniform polarity so that the proper direction of flow of current through the windings a and b of slip relays 24 for pickingup the relay 24 occurs in response to deceleration of the vehicle wheels at a slipping rate.

It should be understood that while we have shown only the equipment for a single car, that a train of connected cars may be similarly equipped. In the case of a train of cars, it is preferable to control the pressure in the control pipe IS in well-known manner by means of. suitable magnet valves On each car the magnet valves being controlled electrically through train wires bination 6 from a master controller located on one car, such as a locomotive, at the head of the train in order to secure simultaneou's'and uniform buildup and reduction of pressure throughout the entire length of the control pipe [5.

Having now described our claimas new and ent,,is: i 1'. In a vehicle brake control system, the comof an electrical relay, means for causin pick-up of said relayonly when a wheel unit of the vehicle rotatively decelerates at a rate 'eX- ceeding a certain slipping rate, means associated with said relay efiective in response to pick-up thereof for maintaining it picked-up until such time as the slipping wheel unit ceases t decelerate at a rate exceedinga second certain rate relatively low compared tothe-rate of deceleration requ red 1 cause i k'l of ere av a d br control means controlled by said relay efiective in re pon e t i k-1 S id la o in a a continued reduction in the degree of application of the brakes associated with said wheel unit 7 to the drop-outer said invention, What we and efiective in response relay to initiate an increase in the degree of application of the brakes.

, 2- n a v h l ake c trol s m t e mbination of an electrical relay, means for causing pick-up of said relay only when a wheel unit of the vehicle exceeding a certain slipping rate, means effective in response to pick-up of said relay for causing said relay to remain picked-up thereafter until such time as the said wheel unit ceases to decelerate at a rate exceeding a second certain rate I relatively low compared to first said certain rate, and brake control means operative in response to the pick-up of said relay for initiating a continued reduction in the degree of application of the brakes associated with said wheel unit at a relatively rapid'rate and effective in response to the dropout of said relay to initiate an increase in the degree in the application of therbrakes at a relatively restrictedrate. i

3. In a yehicle brake control system, the combination of an electrical relay, means-operative in 1 response to the rotative deceleration of any one of a plurality of wheel units of the vehicle at a rate exceeding a certain slipping rate for causing pick-up of said relay, means efiective in response to the pick-up of said relay for maintaining it picked-up thereafter as long as any one of said plurality of wheel units 'rotatively decelerates at a rate exceeding a second certain rate relatively low compared to the first said certain rate, and brake control means operative in response to the pick-up of said relay for effecting a continued reduction in the degree of application of the brakes associated with said pluralityof wheel units at a relatively rapid rate and operative in response to the restoration of the said relay to its dropped-out position for initiating anincrease in the degree of application of the brakes associated with said plurality of wheel units.

4. In a vehicle brake control system, the combination of an electrical relay, means operative in response to the rotative deceleration of any one of a plurality of wheel units of the vehicle at a rate exceeding a certain slipping rate for causing pick-up of said relay, means eiiective in response to the pick-up of said relay for maintaining it picked-up thereafter as long as any one of said plurality of wheel units 'rotatively decelcrates at a rate exceeding a second certain rate desire to secure by Letters Patrotatively decelerates at a rate:

continued reduction in of the brakes associated with said plurality of time relatively low compared to the first said certain rate, and brake control means operative in response to the pick-up of said relay to initiate a the degree of application wheel units at a relatively rapid rate and operative in response to the drop-out of said relay to initiate an increase in the degree of application of the brakes associated with said plurality of wheel units at a relatively restricted rate.

5. In a vehicle brake control system, the pornbination of an electrical relay having a plurality of separate windings, means associated with a plurality of different separately rotating wheel units of the vehicle effective to cause energization of each of said plurality of windings of said relay by a current which is substantially proportional to the rate of rotative deceleration of a corresponding one of said plurality of wheel units, said relay being so constructed and arranged that said relay is not picked-up unless the total ampare-turns of said plurality of windings exceeds a certain value occurring only when one or more of said plurality of wheel units rotatively decelerates at arate exceeding a certain slipping rate, means effective in response to the pick-up of said relay for maintaining said relay picked-up there after for such time as any one of said wheel units rotatively decelerates at a rate exceeding a second certain rate substantially lower than the said certain slipping rate, and brake control means operative while said relay is picked-up for effecting a continuing reduction in the degree of application of the brakes associated with said plural ity of wheel units at a relatively rapid rate and effective in response to the drop-out of said relay for initiating an increase in the degree of the brakes associated with said wheel units.

6. In a vehicle'brake control system, the combination of an electrical relay having a plurality of separate windings, means associated with a plurality of different separately rotating Wheel units of the vehicle efiective to cause energization each of said plurality'oi windings of said relay by a current which is substantially proportional to the rate of rotative deceleration of a corresponding one of sai plurality of wheel units, said relay being so constructed and arranged that said relay is not pickedeup unless the total ampere-turns of said plurality of windings exceeds a certain value occurring only when one or more of said plurality of Wheel units rotatively decelerates at a rate exceeding a certain slipping rate, means eiiective in response to the pick up of said relay for conditioning the relay so that it remains picked-up until the slipping wheel units cease to decelerate at a rate exceeding a sec certain rate substantially lower than said i certain rate, and brake control means opera in response to the pick-up of said relay for e fecting a continuing reduction in the .degr application of the brakes associated with said piurality of wheel units at a relatively rapid rate and effective in response to the drop-out of relay for initiatingan increase in the degree of application of the rakes associatedwith said plurality of wheel units. d

'7. In a vehicle brake control system, the combination of an electrical relay having a plurality of separate windings, means associated with a plurality of different separately rotating wheel units of the vehicle effective to cause energizaticn of each of said plurality of windings of said relay by a current which is substantially proportional to the rate of rotative deceleration of a corresponding one of said plurality of wheel units, said relay being so constructed and arranged that said relay is not picked-up unless the total ampereturns of said plurality of windings exceeds a certain value occurring only when one or more of said plurality of wheel units rotatively decelerates at a rate exceeding a certain slipping rate, a plurality of resistors, means eiiective in the droppedout position of said relay for connecting each of said resistors in shunt relation to a corresponding one of the windings of said relay and effective in response to the pick-up of said relay to disconnect said resistors from shunt relation to said windings, said relay being thereby conditioned in response to the pick-up thereof so that it subsequently drops-out only after the slipping wheel units cease to decelerate at a rate exceeding a second certain rate substantially lower than the first said certain rate, and brake control means operative in response to the pick-up of said relay to initiate a continuing reduction in the degree of application of the brakes associated with said plurality of wheel units at a relatively rapid rate and efiective in response to the drop-out of said relay for initiating an increase in the degree of application of the brakes associated with said plurality of wheel units.

8. In a vehicle brake control system, the combination of a relay having a winding, means for causing energization of the winding of the relay to a degree varying substantially in proportion to the rate of rotative deceleration of a wheel unit of the vehicle, means controlling the current en-- ergizing the winding of the relay in such a manner that the winding is not energized by a current exceeding a certain value and required to cause pick-up of the relay unless the wheel unit rotatively decelerates at a rate exceeding a first certain rate, said current controlling means being effective in response to the pick-up of the relay for causing an increase in the current energizing the winding of the relay for a given rate of rotative deceleration of the wheel unit whereby said relay is restored to its dropped-out condition only after the wheel unit ceases to decelerate at a rate exceeding a second certain rate substantially lower than the first said certain rate, and brake control means operative in response to pick-up of said relay to effect reduction in the degree of application of the brakes associated with said wheel unit and upon restoration to its dropped-out position to efiect an increase in the degree of application of the brakes.

9. In a vehicle brake control system, the combination of an electrical relay having a, winding, means for effecting energization of the winding of said relay by a current substantially proportional to the rate of rotative deceleration of a wheel unit of the vehicle, a, resistor normally shunting the winding of said relay and so controlling the current in the winding of the relay that the current energizing the winding does not exceed a certain value necessary to cause pick-up of the relay unless the said wheel unit rotatively decelerates at a rate exceeding a first certain rate, means effective in response to pick-up of said relay for removing said resistor from shunt relation with respect to the winding of the relay whereby to cause an increase in the current energizing the winding for a given rate of rotative deceleration of the wheel unit and thereby preventing said relay from being restored to its pped-out p tion until the rate of rotative deceleration of the wheel unit reduces below a second certain rate substantially lower than the said fir t certain rate, and brake control means operative during a brak application to effect a rapid reduction in the degree of application of the brakes associated with the wheel unit in response to the pick-up of said relay and operativ to effect an increase in the degree of application of the brakes associated with said wheel unit in response to the restoration of the said relay to its dropped-out position.

10. In a vehicle brake control system, the combination of an electrical relay having a plurality of separate windings, means associated with a plurality of different separately rotating wheel units of the vehicle eilective to cause energization of each of said plurality of windings of said relay by a current which is substantially proportional to the rate of rotativ deceleration of the corresponding one of said plurality of wheel units, means associated with each winding of said relay effective to so control the current in the winding as to necessitate the rotative deceleration of the corresponding wheel unit at a rate exceeding a first certain rate in order to cause pick-up of said relay and effective in response to pick-up of said relay for so increasing the current in the corresponding winding of the relay as to cause the relay to be maintained picked-up thereafter until the wheel un' ceases to rotatively decelerate at a rate exceeding a second certain rate substantially lower than the said first certain rate, and brake control means operative in response to pick-up of said relay for initiating a reduction in the degree of application of the brakes associated with said plurality of wheel units and operative in response to the drop-out of said relay for initiating an increase in the degree of application of the brakes associated with said plurality of wheel units.

11. In a vehicle brake control system, the combination of an electrical relay having a plurality of separate windings, means associated with a plurality of different separately rotating wheel units of the vehicle efiective to cause energization of each of said plurality of windings of said relay by a current which is substantially proportional to the rate of rotative deceleration of the corresponding one of said plurality of wheel units, a plurality of resistors each of which is connected respectively in shunt. relation to a corresponding different one of said windings when said relay is dropped-out whereby to so control the current energizing the respective windings as to necessitate the rotative deceleration of one of the wheel units at a rate exceeding a first certain rate in order to cause pick-up of said relay, said resistors being disconnected from shunt relation to the corresponding windings of the relay in response to the pick-up of the relay whereby to so increase the current in the windings for a given rate of rotative deceleration of the corresponding wheel unit as to maintain the relay in its picked-up position until such time as the corresponding wheel units cease to rotatively decelerate at a rate exceeding a second certain rate substantially lower than the said first certain rate, and brake control means operative in response to the pick-up of said relay for initiating a reduction in the degree of application of the rakes associated with said plurality of wheel units and operative in response to the restoration of said relay to its dropped-out position for initiating an increase in the degree of application of the brakes associated with said plurality of wheel units.

DOUGLAS R. HORST. CLAUDE M. HINES.

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